Mechanical seal



Dec. 11, 1962 F. R. VAN VLEET 3 MECHANICL SEAL Filed 001:. 8. 1959 INVENTOR. FRANK R. VAN VLEET ATTOR N EYS Massachusetts Filed Oct. 8, 1959, Ser. No. 845,271 14 Claims. (Cl. 27727) This invention relates in general to a new and improved shaft seal and in particular to a mechanisal rotary shaft seal.

Basically a mechanical seal of this type consists of a pair of presision-lapped sealing fases which are urged into fluid-sealing, running contact with each other by the applisation of forse to one or both of them. Seals of this kind are generally required to contain a pressurized fluid within ons portion of an enclosure into which a rotatable shaft extends, e.g. the housng of a rotary pump. Generally speaking, the fluid-sealing forse which must be applied to the sealing fases varies with the pressure of the fluid that is to be contained and may not exseed a predetermined value if excessive wear is to be prevented. In fact, the sealing forse is usually kept low enough to permit the entry of a small amount of fluid between the contasting sealing fases in order to form a lubricating film between the fases which further reduces wear. Accordingly, waar of the sealing fases san ossur not only as a result of the applisation of exsessive pressure per se, but also due to the fact that the excessive pressure prevents the formation of a lubrisating film between the contasting sealing fases.

The use of springs asting alone to urge the sealing fases against cash other frequently results in the above-mentioned disadvantages. This is due to the fast that the spring sealing forse must be suflisiently high to withstand the maximum expested fluid pressure. Where the fluid pressure is normally below ts maximum, the spring forse exerted on the contasting surfases is accordingly excessive and produses wear.

The use of springs is subject to further disadvantages owing to the fast that it is extremely difficult to position the contacting spring portion in a plane which is perfectly normal to the axis of the rotating shaft. This holds true whether a number of springs spaced annularly about the shaft are employed, or whether a single spring is used which encirsles the shaft. In either case, spring misalignment produses a pressure variation during cash shaft rotation with the result that the wear on the contasting sealing fases is increased. Excessive wear of the sealing fases permits the compressed springs to expand and thereby aggravates the situation.

The disadvantages associated with the use of springs have been recognized and the pressurized fluid itself, which is to be sontained by the shaft seal, has been employed in order to supplement the spring force. The sealing forse appiied by the fluid is, of course, dependent on the fluid pressure. Frequently, however, the sealing forse due to fluid pressure alone is inadequate for the intended purpose. This oscurs in situations where it is necessary to maintain contact of the sealing fases at low fluid pressures or in the absence of any fluid pressure Whatever, e.g. where it is desired to sonfine the residual fluid to a sertain portion of the housing. In sush sases, springs are still required to maintain the necessary sealing force. As sush, whether supplemented or opposed by the fluid pressure, the spring pressure in presently available rotary, mechanical shaft seals sonstitutes an important portion of the total sealing forse and results in very rapid wear of the sealing fases which nesessitates frequent repair or replasement. Quite apart from the loss of produstion which results from the shut-down of the affested machine,

the sost of a new seal or parts thereof must be sonsidered in this case. In addition, the labor sosts of servicing or replacing the defestive shaft seal, which is usually losated in a relatively inascessible portion of the machine, are high compared to the cost of the seal itself.

Acsordngly, it is the primary object of this invention to provide an improved rotary, meshanical shaft seal whose sontasting sealing fases are subjested to redused wear to permit the seal to operate for long periods of time without the nesessity of servising or replasernent.

The invention relates specifisally to a rotary, mechansal shaft seal for sontaining a normally pressurized fluid within a housing which includes a pair of opposed sealing fases arranged for relative rotational movement. In acsordance with the invention, the fixed forse applied by at least ons relatively weak spring urges the sealing fases into fluid sealing contact with each other when the fluid pressure is low or zero. The sonstrustion is sush that, as normal operating conditions are approashed and the forse due to the pressurized fluid exseeds the fixed spring forse, the spring forse is neutralized and eliminated thus making the sealing engagement of the fases to be due entirely to the forse applied by the pressurized fluid. The spring forse is thus unable to affect the wear of the contasting fases and a seal which has superior performance charasteristics is provided.

This and other -objests of the invention together with further features and advantages thereof will become apparent from the folloWing details spesification when read in connestion with the accompanying drawing, the single FIGURE of which illustrates a preferred embodiment of the invention.

The drawing illustrates the invention in half cross section, the rernaining half having been omitted as self evident due to ts symmetrisal disposition about the shaft axis 22. As rotatable shaft 10 extends through a housing 12 that consists of first and second housing portions 14 and 16 respectively, of which the latter is referred to as the housing gland. The respective housing portions include a pair of mating surfases 18 and 20 which are substantially normal to the aforesaid shaft axis 22. A flat gasket 24 is disposed between the mating surfases to prevent fluid from entering. The housing portions 14 and 16 inslude a pair of interior sylindrisal walls 26 and 28 respectively, having difierent diameters. The wall 28 terminates in a lip 30 which overlies a portion of the wall 26. A rotatable, sylindrisal seal ring 32 of metal is coaxially disposed on the shaft10 and is afixed theretoby means of at least ons set screw 34 so as to rotate with the shaft. The exterior surface 36 of the seal ring 32 defines an annular spase 38 with the interior housing, wall 26 which is open to the pressurized fluid 40. The seal ring 32 further includes an internal, annular slot 42 which fases the shaft 10 and has a radially compressed O-ring 44 disposed therein to prevent the passage of fluid between the shaft and the seal ring 32. A presision-lapped, planar sealing fase 46 which is substantially normal to the shaft axis, terminates one end of the rotatable seal ring 32.

A non-rotating, sylindrisal seal ring helder 48 is soaxially disposed about the shaft 10 and defines an annular spase 5t) with the interior housing wall 28 of the housing gland 16. The seal ring bolder includes an end surface 84 and is axially movable along the shaft while being stationary with respect to the housing gland 16 and shaft rotation. A flange 52 of the seal ring h0lder is disposed opposite the housing lip 30 and defines, a narrow annular passage 54 with the interior housing wall 28 which opens on the annular spase 50. The fiange 52 is defined by a pair of opposed pressure surfases 51 and 53 both norrnal to the shaft axis. The area of the pres sure surfase 51 exseeds that of the pressure surfase 53.

Pateuted Dec. 11, 1962 The flange 52 defines a cylindrical counter bore 56 which accommodates a supplementary non-rotating seal ring 58 that is affixed to the seal ring bolder and which is coaxially disposed about the sbaft 10. Like tbe seal ring bolder With which it moves, the supplementary seal ring 58 is movably in an axial direction but is stationary With respect to shaft rotation. A flange 60 of the supplementary seal ring terminates in a precision-lapped sealing face 62 which is substantially normal to the sbaft axis 22 and which is adapted to maintain a running, fiuid-sealing contact With the sealing face 46 of the rotatable seal ring 32. In a preferred embodiment, the area of the sealing face 62 exceeds the diierential area of the opposed pressure surfaces 51 and 53. The exterior surface of the stationary seal ring 58 defines an annular space 64 With the interior housing wall 26, which connects the annular space 38 and the annular passage 54. A radially compressed ring 66 is disposed in the annular space 50 to prevent tbe passage of the pressurized fluid between the nterior housing wall 28 and the stationary seal ring bolder.

The housing gland 16 furtbcr includcs an internal shoulder 68 substantially normal to the sbaft axis. The shoulder contains a plurality of longitudinal pockets 70 annularly spaced about the sbaft, each containing a relatively weak compresson spring 72. A piston 74 is coaxially disposed about the sbaft axis and is movable in an axial direction but stationary With respect to sbaft rotation. The piston comprises a seating surface 76 which is substantially normal to the shaft axis and which is adapted to bear against the shoulder 68 at one extreme of the axial piston travel. The piston furtber includes a fiange 78 which extends into the annular space 50 and wbose contact surface 80 is adapted to bear against the O-ring 66. An interior piston surface 82 is disposed opposte the end surface 34 of the seal ring bolder and contacts the letter at the other extreme of the piston travel.

In the absence of any pressurized fluid 40, or when the fluid pressure is low compared to the spring pressure, the compressive force exerted by the springs '72 on the piston seating surface 76 prevails to force the piston to theleft in the drawing until the interior piston surface 32 contacts the seal ring bolder surface 34. Simultaneously, the contact surface 80 of the piston bears against the O-ring 66 and pusbes the latter to the left. The dimensions of the annular space 50 are so cbosen that the O-ring is out of contact With the pressure surace 51 at one extreme of the piston travel when the surfaces 82 and 8-4 are in contact With each ot'ner and fluid can rernain in, or enter, the annular space 50. The spring f0rce which is applied to the piston 74 is transmitted to the seal ring bolder 48 and to the non-rotatable seal ring 58 to force the sealing ace 62 of the latter into contact With the sealing face 46 of the rotatable seal ring 32. The sealing force tbus exerted to hold the two sealing faces togetber is sufficent to prevent the entry of fluid tberebetween as long as the fluid is not under any appreciable pressure. As the fluid pressure increases to the normal operating value, the fluid in the annular space 50 forces the O-rng 66 against the contact surface 80 of the piston 78 and thereby drives the piston to the right in the drawing. The axial piston travel continues until the piston "bottoms i.e. until its seating surface 76 is in contact With the shoulder 63. The force exerted on the piston is tbus sufficient to overcorne the spring compression force which continues to be exerted against the seati.ng surface 76. It will be appreciated, however, that the spring force is now without eiect on the sealing faces 46 and 62 and tbis condition continues as long as the forces exerted on the piston by the pressurized fluid exceeds the spring force.

The pressurized fluid furtber exerts a force on each of the opposed pressure surfaces 51 and 53. The net force on the seal ring bolder 48 is to the left in the drawing due to the greater area of the pressure surface 51 and is proportional to the differental area of both pressure suri faces. This force is transmitted to the non-rotatable seal ring 58 where it acts to urge the non-rotatable sealing face 62 into flud-sealing contact With the rotatable sealing face 46.

As previously explained, the area of the sealing face 62 is larger, in the preferred ernbodiment, than the differential area of the pressure surfaces 51 and 53. The sealing force is thus distributed over a larger area which tends to lessen the wear on the sealing faces. The area of the sealing face 62 is cbosen to arrive at the proper unit pressure on the sealing face for a given fluid pressure. in a preferred embodiment, the cbosen unit pressure prevents tbe transfer of the pressurizecl fluid past the sealing faces, while admitting a small amount of fluid to form a Wear-reducing lubricating film.

With the rotary, mechanical seal of tbis invention, tbe spring force is completely ncutralized when the fluid is under pressure and therefore cannot contribute to the wear of the seaiing faces by varying the pressure during each sbaft rotation. Additionally, the fluid is contained witbin 0ne portion of the housing since the sealing fases are at all times in fiuid-sealing contact With each other regardless of sbaft rotation and irrespective of the pressure of the fluid. It will be noted that the sealng faces are urged into fluid sealing contact at all times, even during the transition period when the fluid pressure equals the spring pressure.

T be invention is not, of course, restricted to the partic-- ular configuration of the preferred embodiment which is illustrated berein. For example, in place of a plurality of spring pockets annularly disposed about the shaft 10, a single, centrally located spring pocket which is constricted at one end thereof could be employed in conjuncton With a single compression spring which encircles the shaft 10. Similarly, if it were desired to increase the unit pressure between the sealing faces, the area of the sealing feces 62 could be made smaller than the differential area of the pressure surfaces 51 and 53. The pressure surfaces need net, of course, be normal since the sealing force is determned by the net eiective area upon which pressure is exerted in an axial drection. Sirnilarly, the flange 52 could be extended until the surface 53 forms part of the sealing surface 62. In the latter case, the sealing force would be determined entirely by the fluid pressure exerted on the surface 51. Such a construction is practical where the stationary seal ring and the seal ring bolder are integral.

The invention herein dsclosed provides a. rotary, mechanical shaft seal which relies on a spring force to urge a pair of sealing faces into fluid-sealing contact With each other when the fluid pressure is 10W or zero. Under norrnal operating conditions, the fluid pressure supplies the sealing force to the exclusion of the spring force, the latter being neutralized and hence inelective to cause wear of the sealing faces.

From the foregoing disclosure of the invention it will be apparent that numerous modifications, departures and equivalents will now occur to those sklled in the art, all of which fall within the true spirit and scope of the inventon.

I claim:

1. A mecbanical, rotary sbaft seal for containing a pressurized fluid witbin a portion of a housing wberein a sbaft is disposed, comprising a seal ring disposed on said sbaft and adapted to rotate tberewith, said seal ring baving a first sealing face and furtber including an internal groove encrcling said sbaft, a sealing gasket disposed in said groove adapted to prevent the passage of said fluid between said shaft and said seal ring, said seal ring defining an annular space With said housing open to said fluid, axially movable sealing means disposed about said shaft and being stationary With respect to sbaft rotation, said sealing means including a second sealing face adapted to make running contact With said first sealing face to prevent the passage of said fluid therebetween, said seal ing means defining a second annular space with said housng and a narrow annnlar passage substantially connectng said first and second annular spaces, said sealing means further including a pair of pressure surfaces disposed at opposite ends of said passage, the eective area normal to said shaft aXis of one of said pressure surfaces exceeding the corresponding effective area of the other pressure surface, a second gasket disposed in said second annular space to prevent the passage of said fluid between said housing and said sealing means, said housing including a seating shoulder having at least one pocket, a spring disposed in said pocket and being of such length when compressed as to be completely enclosed in said pocket, an axially movable piston disposed about said shaft and being stationary with respect to shaft rotation, said spring being adapted to urge said piston against said sealing means when the spring pressure exceeds the fluid pressure, said piston extending into said second annnlar space to transmit the spring force to said second-gasket, said pressurized fluid exertng a force on said second gasket in opposition to said spring force to drive said piston into solid contact against said seating shoulder and so neutralizing the pressure of the spring, the force of said fluid applied to the difierential eective area of said pressure surfaces acting to urge said second sealing face into fluidsealing contact with said first sealing face with complete absence of spring pressure.

2. A mechanical, rotary shaft seal for containing a pressurized fluid within a porton of a housing wherein a shaft is disposed, comprising first and second sealing means disposed within said housing and interiorly spaced therefrorn, said first sealing means including a first sealing face adapted to rotate with said shaft, a gasket disposed between said first sealing means and said shaft to prevent the passage of said fluid therebetween, second sealing means movably disposed in the direction of the shaft axis but being statonary with respect to shaft rotation, said second sealing means ncluding a second sealing face adapted to contact said first sealing face and further comprising opposed pressure surfaces exposed to said fluid, a gasket disposed between said second sealing means and said housing to prevent the passage of said fluid therebetween, said housing including an internal shoulder containing at least one axially extending pocket, an axally movable piston stationary with respect to shaft rotation, a spring disposed in said pocket, said spring being of such length when compressed as to be completely enclosed therein and when not so enclosed being adapted to exert an axially directed force on said piston to urge the latter against said sealing means when the spring pressure exceeds the fluid pressure, said piston being further adapted to transmit the spring force to said second gasket, the force of said pressurized fluid on said second gasket acting in opposition to said spring force to urge said piston into contact with and against said shoulder and so neutralize the action of the spring, the fluid force acting on the effective differential area of said opposed pressure surfaces acting in the absence of spring pressure to force said second sealing face into fluid-sealing contact with said first sealing face to admit sufficient fluid only to form a lubricatng film between said sealing faces.

3. A rotary shaft seal for containing a pressurized fluid within a portion of housing into which a shaft extends, comprising first sealing means coaxially disposed about said shaft within said housing and interiorly spaced from the latter, said first sealing means including a first sealing surface adapted to rotate with said shaft, a first gasket disposed between said first sealing means and said shaft to prevent the passage of said fluid therebetween, second coaxally disposed sealing means interiorly spaced from said housing and including a second sealing surface, said second sealing means being movably disposed in the direction of the axis of said shaft bnt being stationary with respect to shaft rotation, said second sealing means including an efiectve presusre area norrnal to said axis exposed to said pressnrized fluid, the fluid force on said eective pressure area being adapted to urge said second sealing surface in a first axal direction into fluid sealing contact with said rotatable first sealing -surface, a second gasket disposed between said second sealing means and said housing to prevent the passage of said fluid therebetween, an axially movable piston coaxally disposed about said shaft and being stationary with respect to shaft rotation, said housing including a shoulder containing at least one pocket, a compression spring disposed in said pocket and being of such length when compressed to be totally enclosed therein, said spring when uncompressed being adapted to urge said piston resiliently against said second sealing means in said first axial direction when the fluid pressure is below a predetermined value, said fluid being adapted to force said second gasket against said piston in the opposite axial direction when said fluid pressure exceeds said predetermined value to drive said piston into engagement with said shoulder and so eliminate completely and temporarily the action of said compression spring.

4. The apparatus of claim 3 wherein said shoulder has a plurality of pockets coaxially spaced about said shaft, each of said pockets Containing a compression spring adapted to bear against said piston.

5. 'I'he apparatus of claim 3 wherein said pocket consists of a bore coaxially surrounding said shaft and having a constriction at one end thereof, said springbeing seated on said constriction while encircling said shaft and being adapted to bear against said piston.

6. Apparatus according to claim 3 wherein said second sealing means includcs first and second opposed pressure surfaces snbstantally norrnal to the shaft axis, said second pressure surface facing said second gasket and having an area exceeding that of said first pressure surface by an amount eqnal to said erective pressure area.

7. Apparatus according to claim 6 wherein said effec tive pressure area is smaller than the area of said second sealing surface.

8. A mechanical, rotary shaft seal for containing a pressurized fluid within a portion of a housing into which a. shaft extends, comprising a rotatable seal ring coaxially affixed to said shaft to rotate therewith, said ro tatable seal ring being spaced from the interior walls of said housing, a radially compressed O-ring disposed between said rotatable seal ring and said shaft to prevent the passage of fluid therebetween, a stationary seal ring bolder coaxially disposed about said shaft so as to be axially movable but stationary with respect to shaft rotation, said stationary seal ring holder including a flange having a pair of opposed pressure surfaces whose difierential area defines a net eiective pressure area responsve to axially directed fluid pressure, a stationary coaxial seal ring aflxed to said seal ring bolder and axially movable therewith, said rotatable and stationary seal rings being spaced from oppositely disposed interior surfaces of said housing and comprising respectively rotatable and stationary sealing faces adapted to be in running fluid-sealing contact with each other, a radially compressed O-ring disposed between said sta tionary seal ring bolder and one of said interior housing surfaces, one side of said O-ring facing oneof said presusre surfaces, a piston coaxally disposed about said shaft so as to be axially movaole but being stationary with respect to shaft rotation, said piston including a flange adapted to contact the other side of said lastrecited O-ring, said housing inclnding an interior sholder having at least one pocket, a compression spring disposed in said pocket and being of such length when compressed as to be totally enclosed therein, said spring being adapted when uncompressed to f0rce said piston against said seal ring bolder in a first axial direction in order to urge said statonary sealing face againstsaid rotatable sealing face when the fluid pressure is below a predetermined value, sad fluid being adapted to force sad last recited O-ring in the opposite axial direction when sad fluid pressure exceeds sad predetermined value to drive sad piston against sad shoulder and thus neutralizing the action of the spring, the force of sad fluid on sad net eifective pressure area being adapted to urge sad stationary sealing face in sad first direction into fluid-sealing contact with sad rotatable sealing face and in complete absence of spring pressure.

9. A mechanical, rotary sbaft seal for containing a pressurized fluid in a portion of a housing into which a sbaft extends, comprising a rotatable seal ring coaxially disposed on sad shaft to rotate therewith, a first annular space open to sad pressurized fluid defined by sad rotatable seal ring and an interior surface of sad housing, sad rotatable seal ring includng a sealing face .substantially normal to the axis of sad shaft, a radially compressed Q-rng disposed between sad rotatable seal ring and sad sbaft to prevent the passage of fluid tbere between, a stationary seal ring bolder coaxially disposed about sad shaft and defining a second annular space with another interior surface of sad housing, sad seal ring bolder being movably disposed in an axial direction but being stationary with respect to shaft rotation,

-said seal ring bolder includng a flange which defines a narrow annular passage with sad other interior housmg surface open te sad second annular space, a stationary coaxial seal ring aflixed to sad seal ring bolder so as to be axally movable therewith, sad seal ring bolder defining a third annular space with sad first recited interior housing surface which connects sad first annular space and sad annular passage, sad stationary seal ring includng a sealing face substantially normal to sad shaft axis and adapted to make running contact with sad first recited sealing face, sad seal ring bolder flange includng first and second pressure surfaces substantially normal to sad shaft axis and facing sad second and third annular spaces respectively, the area of sad first pressure surface exceeding that of sad second pressnre surface, a radially compressed O-ring disposed in sad second annular space out of contact with sad first pressure surface, a piston coaxially disposed about sad shaft and includng a flange extcnding into sad second annular space, sad last recited flange having a contact surface adapted to bear against sad O-ring disposed in sad second annular space, sad piston being axially movable but being stationary with respect to shaft rotation and further includng a seating surface substantially normal to sad shaft axis, sad housng comprising an internal shoulder substantially normal to sad shaft axis and includng at least one pocket, a

compression spring disposed in sad pocket and being of such length when compressed as to be totally enclosed therein, sad spring being adapted when uncornpressed to bear against sad piston seating surface and to force sad piston against sad seal ring bolder in a first axial direction in order to urge sad sealing faces into fluid-sealing contact with each other when sad fluid pressure is below a predetermined value, sad fluid being adapted to force the -ring in sad second annular space in the opposite axial direction against sad piston contact surface when sad fluid pressure exceeds sad predetermined value until sad piston seating surface contacts sad interior shoulder thereby neutralizing the action of the spring, the force applied by sad fluid on the diflerential area of sad pressure surfaces being adapted to drive sad seal ring bolder in sad first axial direction so as to urge the sealing face of sad stationary seal ring into fluid-sealing contact with the sealing face of said-rotatable seal ring and in absence of all spring pressure.

1(). The apparatus of claim 9 wherein sad internal housing shoulder comprises aplurality of pockets co- :axially spaced abo ut sad shaft, each of sad pockets con- 8 taining a compression spring adapted to bear against sad piston seating surface.

11. The apparatus of claim 9 wberein sad pocket consists of a bore coaxially surronnding sad shaft and having a constriction at one end thereof, sad spring being seated on sad constriction while encircling sad shaft and being adapted to beat against sad piston seating surface.

12. The apparatus of claim 9 wherein the area of the sealing face of sad stationary seal ring excecds the differential area of sad pressure surfaces.

13. A mecbanical rotary shaft seal for containing a pressurized fluid within a portion of a housing into which sad shaft extends, sad housing comprising first and second portions having first and second interior, cylindrical walls coaxially disposed about sad shaft, sad second cylindrical wall having a smaller diameter than sad first cylindrical wall and includng -a lip portion ovcrlying sad first cylindrical wall, a rotatable cylindrical seal ring coaxially disposed on sad shaft, means for afiixing sad seal ring to sad sbaft so as to rotate therewith, sad seal ring includng an internal, annular groove facing sad shaft, a first, radially compressed -ring disposed in sad groove to prevent the passage of oil between sad stationary seal ring and sad shaft, the extcrior surface of sad seal ring defining a first annular space with sad first interior housing wall open to sad pressurized fluid, sad seal ring includng an annular sealing face substantially normal to sad sbaft axis, a stationary cylindrical seal ring bolder coaxially disposed abont sad shaft and having an exteror surface whicb defines a second annular space with sad second interior housing wall, sad seal ring bolder being axially movable but being stationary with respect to shaft rotation, sad seal ring bolder includng a coaxially disposed annular flange, the exterior surface of sad annular flange defining a narrow annular passage with sad lip portion open te sad second annular space, acoaxially disposed, cylindrical stationary seal ring fixedly positioned within sad flange and axially movable with sad seal ring bolder, sad stationary seal ring defining a third annular space with sad first internal housing wall which connects sad first annular space and sadannular passage, said stationary seal ring includng an annular flange which terminates in a second sealing face substantially normal to sad shaft, sad second sealing face having an area smaller than sad first sealing face and being adapted to make running contact with the latter, sad annular flange of sad seal ring bolder includng first and second pressure surfaces substantially normal to sad shaft axis and facing sad second and third annular spaces respectively, the area of sad first pressure sur face exceeding that of sad second pressure surface by an amount less than the area of sad second sealing -face, a second radially compressed O-ring disp:sed in sad second annular space out of contact with sad first pressure snrface, a coaxially dsposed, cylindrical piston to sad shaft axis, sad second housingporticn includng an internal sboulder substantially normal to sad shaft axis and includng at least one pocket, a compression spring disposed in sad pocket and being of such length when compressed as to be totally enclosed tbere in, sad spring being adapted when uncompressecl to beat against sad piston seating surface and to orce sad piston against sad seal ring bolder in a first axial di rection when the fluid preSsure is below a predetermined value in order to maintain sad sealing faces in fluidsealing contact with each other, sad fluid being adapted to force the O-ring in sad second annular space against 9 10 sad pston contact surface in the opposte axial direccomprses a plurality of pockets coaxally sp-aced about ton when sad flud pressure exceeds sad predetermned sad shaft, each of sad pockets containng a compresson value untl sad pston seatng surface contacts sad ntespring adapted to bear against sad pston seating surror shoulder thereby neutralizng the acion of the face. spring, the force applied by sad flud on the derental area of sad pressure surfaces beng adapted to drive Refeellces CW I1 he fi1e of hS Ptfint sad seal ring helder in sad first axial drecton to urge UNITED STATES PATENTS sad second sealng face nto fluid-sealng contact with 2,128744 Hornschuch A11I. 30, 1938 :;ifirst seahng face In the absence of all spnng pres 10 2,1 56,719 Berger May 2, 1939 14. The apparatus of claim 13 wherein sad shoulder 2470419 Voytech May 1949 2,503,086 Albrght Apr. 4, 1950 

